Subject:

Abstract:

Recruitment through seeds is a critical process in the life history of plants. Better knowledge about this process may be helpful in predicting species ranges and range shifts under climate change.
In western Norway, the climate is predicted to become warmer and wetter. In the Norwegian fjord landscape, precipitation increases from the continental fjords to the oceanic coast, and temperature increases from alpine to lowland. Recruitment was investigated in 12 sites which provide a climate grid", where effects of precipitation and temperature on recruitment can be explored independently.
Gap availability is the main requirement for maintaining diversity in plant communities. Generating gaps by inducing disturbance provides an opportunity for recruitment from seeds present in the seedbank, in the intact vegetation or by invasion through long-distance dispersal. Ninety-six gaps were created, and 5077 seedlings were recorded and id-tagged.
The number of seedlings emerging in the climatic grid" was influenced by both precipitation and temperature, but also local factors including such as insulation and inclination were important. Seedlings responded to temperature at different levels depending on the precipitation regime. The effect of temperature on seedling emergence in closed vegetation shifted along the precipitation gradient. In wet areas the effect was negative, whereas in dry areas the effect was positive. In disturbed treatments the number of emerged seedlings increases with temperature along the entire temperature gradient, and do not show the same negative effect of precipitation as in the undisturbed treatments.
Findings from two comparable methods estimating dispersal sources imply that seedbank are the main source to seedling recruitment, and show a tendency towards a higher contribution in drier areas. Findings based on the recruit-tag approach estimate a seedbank contribution of 23% - 89%. The same approach was used to estimate the extent of long-distance dispersal across elevation categories. The vast majority of the seedlings were dispersed only short distances, however 2.8% of the total emerging seedlings are potentially long-distance dispersed.